1. Field of the Invention
This invention relates to an improved apparatus for continuously casting metals and, in particular, special steels.
2. State of the Art
In the manufacture of special steels, as well as that of ordinary steels, a molten steel can be cast by continuous casting into cast pieces in the majority of cases. Due to the fact that the cast pieces can be readily separated, continuous casting is advantageous for providing a high yield of a rolled steel product. Namely, the cast portions of a steel strand which are obtained continuously can be cut off at their respective longitudinal end portions. Accordingly, when casting steels of different kind, it is advantageous that each strand is cast as close as possible to the next strand. This is called continuous-continuous casting.
A continuous casting apparatus for a multistrand system which is used industrially employs a water-cooled mold for providing a plurality of strands of casting material. In this apparatus, a molton steel is transferred from a ladle to a tundish and cast concurrently by the water-cooled mold. This apparatus provides enhanced continuous casting, because the duration of time for casting of each ladle can be shortened, and because problems due to temperature drop of the molten metal can be minimized. With this apparatus the number of strands cast varies according to factors such as type of steel, strand sectional size, drawing speed and so forth. This system normally can cast 2 to 8 strands, however, a typical apparatus will cast 4 strands.
The kinds of steel kind for mass production by such multistrand system continuous casting apparatus are preferably those which can take advantage of the continuous casting. For example, a molton steel in a 80-ton ladle can be cast in 4 charges on a 4-strand apparatus. However, special steel or specialty steels are usually cast in a small-lot, and a molten steel of 80 tons can be cast in only one charge. In this situation a deterioration in yield is unavoidable when casting on the 4-strand apparatus. This is due in part to the fact that small lot of a special steel generally contains a significant amount of an expensive alloying component, making it is desirable to obtain a high yield based upon the requirements of saving resources, as well as saving energy and decreasing costs.
On the other hand, a continuous casting apparatus requires a great deal of investment in equipment and, therefore, it is preferable that such an apparatus be used at a high rate of operation even when casting special steel.
Recent large-scale steel foundries employ various types of smelting apparatuses, such as a convertor, an arc furnace, an AOD furnace, a LF furnace and the like, based on the kind of steel to be manufactured. These apparatuses are generally used for preparing more than one kind of steel. Under such circumstances, it is desirable that the foundries be operated to harmonize the yield of steel with a rate of operation for all kinds of steels, including special steels.